This instrument (CIS: Cluster Ion Spectrometry) is capable of obtaining full 3D ion distributions with high time resolution (in one spacecraft spin) and mass-per-charge resolution. The experiment consists of two different instruments, a Hot Ion Analyzer (HIA) and a time-of-flight Ion Composition and Distribution Function analyzer (CODIF). Extensive on-board processing is done, within its dual-processor Data Processing System (DPS). For more details of the Cluster mission, the spacecraft, and its instruments, see the report Cluster: mission, payload and supporting activities,'' March 1993, ESA SP-1159, and the included articleThe Cluster Ion Spectrometry Experiment,'' by H. Reme et al., from which this information was obtained.